This invention relates to electrical interconnects, and, more particularly, to high reliability electrical make/break connectors such as those used in thermal ink jet printers with replaceable print cartridges.
Printers are devices that print images onto a printing medium such as a sheet of paper. Printers of many types are available, and are commonly linked to a computer that supplies the content of the images, in the form of text, characters, or figures, that are to be printed.
An ink jet printer forms small droplets of a colorant such as an ink or a dye that are ejected toward the printing medium in the pattern that forms the images. Ink jet printers are fast, producing a high output of print, and quiet, because there is no mechanical impact during formation of the image, other than the deposition of the ink onto the medium.
One type of ink jet printer, the thermal ink jet printer, has a large number of individual colorant-ejection nozzles in a print head, oriented in a facing, but spaced-apart, relationship to the printing medium. There is an electrical resistor adjacent each nozzle, and a pulse of current through the resistor causes ejection of a droplet of colorant from the nozzle toward the medium. The print head moves relative to the surface of the medium, with the nozzles ejecting droplets of colorant under command at the proper times. The droplets strike the medium and then dry to form "dots" of colorant that, when viewed together, create the permanently printed image.
Most thermal ink jet printers are constructed with a permanent printer body and a printing means. The printing mechanism includes, preferably, a disposable print head cartridge containing both the colorant ejector and the colorant supply (or, alternatively, a permanent colorant ejector with a disposable colorant supply). The printer body contains the mechanisms to support the printing medium and the print head cartridge in the proper facing relationship so that printing can be accomplished, the power supply that supplies the electrical current to the ejector resisters, the electronic controllers to achieve particular printing functions, and the interface to the computer. The disposable print head cartridge includes the ejector mechanism, its support, and in some cases the colorant supply. There must be a make/break interconnect between the printer body and the disposable print head cartridge, which is a connection that is readily made, is "temporary" in the sense that it is maintained until the cartridge is to be replaced, and allows easy disconnection and replacement. The present invention is concerned with such a make/break interconnect.
By experience with commercial thermal ink jet printers, the make/break interconnect has been found to be one of the portions of the system most susceptible to reduced reliability in service. The work leading to the present invention has determined that the reduced reliability may be traced to two principal causes. First, the electrical interconnections may be formed slightly irregularly as a result of normal manufacturing tolerances. Even relatively small irregularities in height and position of the interconnections may prevent a contact from being achieved on all of the lines of each interconnect. The result is that manufacturing tolerances must be reduced, with resulting increased manufacturing cost and increased rejection rates. Quality control procedures must be more extensive than would otherwise be required. Second, the electrical interconnections may become dirty or oxidized during storage prior to installation, or even after installation. The person installing the print head cartridge or using the thermal ink jet printer must take extra care to clean the interconnections prior to use, or at intervals during use. This requirement is burdensome, because most users are not technically qualified and may actually damage the interconnection during the cleaning process. The alignment and dirt/contamination problems become more troublesome as the number of required connections increases, as is the trend in modern printers.
There is therefore an ongoing need for an improved approach to a make/break interconnection for ink jet printers and other devices that is more tolerant of misalignment and other consequences of normal manufacturing tolerances, and also is less susceptible to reduced reliability due to the presence of dirt or contamination. The present invention fulfills this need, and further provides related advantages.